The power steering gear with the distributing valve in the piston, as disclosed and claimed in my previous basic mechanical U.S. Pat. No., Sheppard, 3,092,083, Piston For Power Steering System, has been a highly successful design and, in fact, is reputed to have the highest efficiency and reliability, and the lowest manufacturing cost in the industry. The basic design has been utilized in several models and sizes since its introduction in the early 1960's. Certain refinements, some of which are patented, have been made over the years in the Sheppard Power Steering System, but up until now the basic design of the piston and the steering gear has remained substantially the same.
Over the past few years, automotive manufacturers, including truck manufacturers, have increasingly been making the space under the front end of the vehicle more and more crowded with the addition of more accessory equipment, and larger and stronger axles, engines and other components. Compounding the space problem, has been the need to trim weight from a given size vehicle in order to increase the payload and to minimize cost and fuel usage. Truck manufacturers have included in their redesigns, shortening the chassis of the vehicle, and particularly the front end. All of this has inevitably led to engineering difficulties in effecting the mechanical interconnection of the steering shaft of the vehicle to the input shaft of the steering gear. That is, the space between the mating ends of the shafts has been so shortened and otherwise crowded that universal joints on standard steering gears are not longer workable, thereby forcing the need of alternative joints, such as the more expensive miter gear boxes.
Thus, the need has arisen for reducing the size and weight of the power steering unit, and particularly for shortening the input shaft end, while at the same time increasing its efficiency to handle the larger and larger vehicles with greater payloads.
Other major areas of change needed to accomplish the desired improved results in my new power steering gear are: (1) improving the manufacturing capability and efficiency through change of structure, particularly in the piston and bearing cap; (2) providing improved reversibility in the valve; (3) providing improved reversibility in the operating piston; and (4) providing structure for full volume fluid transfer without unwanted bleeding between high and low pressure feed ports.